CID Electromagnetic Compatibility & EMI Control 2

Question 1

In CISPR 32 and FCC Part 15 emissions testing, what is the key difference between Class A and Class B limits?

Accepted Answer

Class B limits are stricter and apply to residential equipment; Class A applies to commercial/industrial

Answer

Class A limits are stricter and apply to residential equipment; Class B applies to industrial

Answer

Both classes have identical limits but differ in measurement distance

Answer

Class A covers conducted emissions only; Class B covers radiated emissions only

Question 2

A common-mode choke in a cable assembly primarily attenuates:

Accepted Answer

Common-mode currents flowing in the same direction on both conductors

Answer

Differential-mode signals intended to travel along the cable

Answer

The DC resistance of the cable

Answer

The characteristic impedance of the transmission line

Question 3

What is the primary EMC advantage of a multilayer PCB with dedicated ground and power planes over a two-layer board?

Accepted Answer

Reduced loop inductance of the power distribution and signal return paths

Answer

Lower manufacturing cost and simpler assembly

Answer

Easier visual inspection of all traces

Answer

Higher trace current-carrying capacity due to more copper layers

Question 4

Which cable routing technique most reduces radiated emissions from an interconnect cable acting as an unintentional antenna?

Accepted Answer

Bundling cables together and routing them tightly along a grounded chassis

Answer

Routing cables in free air away from the chassis

Answer

Increasing the length of the cable to reduce its resonant frequency

Answer

Using high-gauge wire to increase the cable's DC resistance

Question 5

When performing conducted emissions measurements per CISPR standards, a LISN (Line Impedance Stabilization Network) is used to:

Accepted Answer

Provide a defined, repeatable impedance at the AC input of the EUT and couple EMI to the measurement receiver

Answer

Filter all noise from the AC power line before it reaches the EUT

Answer

Supply regulated DC power to the equipment under test

Answer

Simulate the impedance of a transmission line on the PCB

Question 6

A ferrite bead placed in series on a power supply line in a PCB design primarily provides:

Accepted Answer

Low impedance to low-frequency DC power while presenting high impedance to high-frequency noise

Answer

A low-pass filter for signals below 1 MHz

Answer

A means of increasing the inductance of a differential pair

Answer

A surge protection device for electrostatic discharge events

Question 7

Which statement correctly describes the relationship between a signal's edge rate (rise/fall time) and its EMI potential?

Accepted Answer

Faster edge rates produce higher-frequency harmonic content and generally increase radiated EMI

Answer

Slower edge rates generate more high-frequency harmonics and greater EMI

Answer

Edge rate has no effect on the frequency spectrum of EMI emissions

Answer

Only the signal amplitude, not the edge rate, determines EMI magnitude